In the art of electrical machining it has long been recognized that noxious or harmful gases are generated from a machining gap across which an electric current is supplied between a tool electrode and a workpiece to erosively remove material from the workpiece. The machining gap is flooded with a machining liquid medium which is decomposed into these gases as a result of passage of the machining electric current. In electrical discharge machining (EDM), for example, the machining liquid can advantageously be kerosene, transformer oil or like hydrocarbon which is decomposed to generate, among others, gaseous components (e.g. propane, hexane, benzene, etc) which are toxious and also inflammable. While an EDM machining liquid primarily composed of water which is harmless and not inflammable may be employed, it has been found to be desirable that the water liquid should, for the sake of increasing the machining efficiency, include some proportion of one or more of these hydrocarbons, or silicone oil which upon decomposition emits gaseous components such as carbon monoxide which are again hazardous to life and the environment. In electrochemical machining (ECM), electrochemical-discharge machining (ECDM), electrochemical grinding (ECG) and electrochemical-discharge grinding (ECDG) processes, nitride, nitrate and carbonate salts are known to be principal or additive electrolytic compounds which assure excellent machining results but upon electrolytic or discharge decomposition yield nitrogen oxides (NOx) and carbon monoxide which are toxic.
In the conventional electrical machining equipment, these noxious or harmful gases are either simply allowed to be emitted, causing pollution of the atmosphere in the region of the equipment, or are treated at a considerable cost but only with limited results as to detoxification or innocuousness.